April 23, 2010

Study Looks At Epic Asian Droughts

The most detailed picture of at least four epic droughts that Asia has seen in the past 1000 years was found in the study of tree rings, scientists reported on Thursday.

Scientists collected data over a 15 year period that they expect will reveal a better understanding of how climate change can unleash large-scale weather disruptions.

Severe shifting in the seasonal monsoon rains in Asia, which feed almost half the world's population by producing crop growth, could affect socio-economics in a serious way, according to scientists at Columbia University's Lamont-Doherty Earth Observatory.

Droughts from past times were mapped out by studying the rings of thousands of ancient trees all across Asia. Among them was a drought in 1644 that may have contributed to the downfall of the Ming Dynasty and another in the 1870s that caused millions of people to starve to death.

Edward Cook, head of Lamont's Tree Ring Lab, said that global climate models have failed to "accurately simulate the Asian monsoon." The limitations have hampered the ability for scientists to plan for future, potentially rapid and unexpected shifts in a warming world, he told AFP.

Scientists pointed to evidence that shows changes in the monsoons are driven partly by variations in sea-surface temperatures, with some speculation that warming trends may modify and possibly intensify these cycles.

Prior to the study, reliable data collected throughout Asia only dated back to 1950.

The tree-ring records suggest that climate may have contributed to the fall of the Ming Dynasty in 1964. The finding adds to additional evidence of a severe drought already referenced in some historical Chinese texts as the worst drought in 500 hundred years at the time.

The study shows that the drought occurred at some point between 1638 and 1641. Northern China was most severely affected. Ramifications of the drought are believed to have fueled rebellions by farmers that eventually contributed to the fall of the dynasty.

The annual growth rings in some tree species are determined by rainfall. Researchers searched over 300 sites throughout Asia looking for ancient trees old enough to provide long-term evidence they needed. The trek took them through Siberia, Indonesia, northern Australia, Pakistan and parts of Japan.

University of Hawaii meteorologist Bin Wang said the tree-ring study will prove valuable to monsoon forecasting, allow forecasters to detect short-term and long-term patterns thanks to the detailed range and length of the record.

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Image 1: Tree ring scientists Ed Cook (left) and Paul Krusic trekked for nearly two weeks to reach this 1,000 year old hemlock in the Himalayas of Nepal. Credit: Brendan Buckley.